1. Field of the Invention
The present invention relates to a method and apparatus for testing the filtration efficiency of cloth materials intended for use in a clean room environment, and further includes a method for determining the useful life of dust free clothes made from the cloth materials based on calculating the filtration efficiency of the materials.
2. Description of the Related Art
It is well known that semiconductor fabricating processes must be carried out in a clean room environment where clean air is continuously introduced. However, the presence of dust particles in the air causes contamination that may corrupt the high density and minute sized semiconductor devices. Recent efforts to improve semiconductor fabrication techniques focused on the maintenance and control of the cleanliness of the clean room by eliminating those factors that generate dust particles which adversely affect production yield, production reliability, and product quality.
Dust particles may be generated by, for example, processing equipment or expendable supplies which are used in the clean room. Clean room operators themselves are a source of particle contamination because the operator continuously generates dust by moving about the clean room as he or she works. The semiconductor chip processing equipment and the expendable supplies have been improved to the extent that they rarely generate any particle contamination. It is the operator who has become the primary source of dust particle contamination that affects the quality of semiconductor devices fabricated in a clean room environment.
Ideally, semiconductor devices should be fabricated automatically without any human intervention, however, this is impossible at the present time given the present state of the art. Therefore, efforts are continually concentrated on performing the manufacturing processes with minimum intervention by the operator, while at the same time seeking to suppress particle generation whenever human intervention is still required.
The operator working in a clean room wears dust free clothes made from cloth materials specifically designed and intended for use in a clean room environment, e.g., dust free garments, dust free masks, and dust free gloves. The ability of the material to filter, i.e. impede or block, the passage of dust particles through the material is known as filtration efficiency. To enhance the filtration efficiency of the dust free clothes worn by the operator, highly efficient cloth materials with high filtration efficiency are desirable.
As clothes made from dust free cloth age, their filtration efficiency is reduced causing them to loose their ability to filter or impede the passage of contaminating dust particles generated by body of the operator. As a result, the contaminating particles are released into the environment. Clothes made from material that has exceeded its useful life therefore become a source of particle contamination in the clean room. Accordingly, it is necessary to accurately test the filtration efficiency of the dust free clothes to determine their useful life. Similarly, the filtration efficiency of newly developed cloth materials intended for use in a clean room environment can be calculated in order to determine their suitability for such use.
Therefore, a need exists for an apparatus designed for testing the filtration efficiency of cloth materials intended for use in a clean room environment, especially one which is also suitable for use inside the clean room itself.